System and Method for Temperature Estimation in an Integrated Motor Drive

ABSTRACT

A system to monitor the temperature of power electronic devices in a motor drive includes a base plate defining a planar surface on which the electronic devices and/or circuit boards within the motor drive may be mounted. The power electronic devices are mounted to the base plate through the direct bond copper (DBC). A circuit board is mounted to the base plate which includes a temperature sensor mounted on the circuit board proximate to the power electronic devices. The temperature sensor generates a digital signal corresponding to the temperature measured by the sensor. A copper pad is included between each layer of the circuit board and between the first layer of the circuit board and the sensor. The circuit board also includes vias extending through each layer of the board. The copper pads and vias establish a thermally conductive path between the temperature sensor and the base plate.

BACKGROUND OF THE INVENTION

The subject matter disclosed herein relates generally to temperatureestimation in a motor drive and, more specifically, to an improvedsystem for monitoring the temperature of power electronic devices in anintegrated motor drive.

As is known to those skilled in the art, motor drives are utilized tocontrol operation of a motor. The motor drive is configured to controlthe magnitude and frequency of the output voltage provided to the motorto achieve, for example, a desired operating speed or torque. Accordingto one common configuration, a motor drive includes a DC bus having a DCvoltage of suitable magnitude from which an AC voltage may be generatedand provided to the motor. The DC voltage may be provided as an input tothe motor drive or, alternately, the motor drive may include a rectifiersection which converts an AC voltage input to the DC voltage present onthe DC bus. The motor drive includes power electronic switching devices,such as insulated gate bipolar transistors (IGBTs), thyristors, orsilicon controlled rectifiers (SCRs). The power electronic switchingdevice further includes a reverse conduction power electronic device,such as a free-wheeling diode, connected in parallel across the powerelectronic switching device. The reverse conduction power electronicdevice is configured to conduct during time intervals in which the powerelectronic switching device is not conducting. A controller, such as amicroprocessor or dedicated motor controller, generates switchingsignals to selectively turn on or off each switching device to generatea desired DC voltage on the DC bus or a desired motor voltage.

It is also known that each of the power electronic devices has certaininherent power losses, such as conduction losses and switching losses.Thus, as each of the power electronic devices conducts current or as itis turned on and off, power is dissipated as heat within the device. Inorder to prevent device failure, it is desirable to monitor the junctiontemperature of the power electronic devices.

Historically, motor drives have been mounted in control cabinets at alocation separated from the motor which it is controlling. The motordrives typically utilize power modules which contain the powerelectronic devices. A power module may include, for example, six IGBTsand their respective free-wheeling diodes (FWDs). The IGBTs and FWDs areenclosed within a plastic housing and terminals are provided toestablish an electrical connection between each power electronic deviceand the DC bus and/or the motor. Also enclosed within each module may bea thermistor to monitor the temperature of module.

However, developments in the power electronic devices used to controlthe motor have reduced the size of the components. This reduction insize of the power electronic devices along with a desire to reduce thesize of the control enclosures have led to placing at least a portion ofthe motor controller electronics on the motor itself as an integratedmotor drive. Specifically, the inverter section, which converts the DCvoltage on the DC bus to the AC voltage supplied to the motor, ismounted on the motor. Because the motors are typically located on amachine or within an industrial process line, it is desirable to use anenclosure for the integrated motor drive which has a footprint equal toor less than the area of the surface on the motor to which it is mountedand which has a low profile, and conventional power modules may not fitwithin the desired enclosure.

As a result, motor controllers have been developed in which individualpower electronic devices are mounted within the housing to form aninverter section. The individual power electronic devices may be mountedin a smaller area than traditional power modules. However, byeliminating the traditional power module, the thermistor is no longerpresent. Providing a separate thermistor within the integrated motordrive has its drawbacks. The thermistor generates an analog signal thatis susceptible to interference from modulation of the power electronicdevices. Further, the analog signal requires conversion of the signal toa digital signal prior to being input to a controller and isolation ofthe signal from the controller. Finally, the signal generated isnon-linear and requires calibration and compensation within thecontroller.

Thus, it would be desirable to provide an improved system and method formonitoring the temperature of power electronic devices in an integratedmotor drive.

BRIEF DESCRIPTION OF THE INVENTION

The subject matter disclosed herein describes a system to monitor thetemperature of power electronic devices in a motor drive and, morespecifically, the junction temperature of power electronic devicesutilized in an integrated motor drive. The motor drive includes a baseplate, typically a copper base plate, defining a planar surface on whichthe electronic devices and/or circuit boards within the motor drive maybe mounted. The power electronic devices are mounted to the base platethrough the direct bond copper (DBC). A circuit board is mountedproximate to the power electronic devices and includes solder padsconfigured to establish electrical connections between the powerelectronic devices and the control and power circuits in the integratedmotor drive. These electrical connections conduct, for example, theswitching signals to control operation of the power electronic devicesas well as the DC voltage from the DC bus through the power electronicdevice to the motor. A temperature sensor is mounted on the circuitboard proximate to these solder pads and, therefore, proximate to thepower electronic devices. The temperature sensor generates a digitalsignal corresponding to the temperature measured by the sensor. Thecircuit board may be single layer, but is more commonly a multi-layerboard. A copper pad is included between each layer of the circuit boardand between the first layer of the circuit board and the sensor. Thecircuit board also includes multiple vias extending through each layerof the board between temperature sensor and the base plate. Each viaincludes a thermally conductive material such as copper lining its innerperiphery. Optionally, each via may be filled with a thermallyconductive material, such as solder. The copper pads and vias establisha thermally conductive path between the temperature sensor and the baseplate having known or controlled thermal characteristics.

According to one embodiment of the invention, a temperature detectionsystem for estimating a junction temperature of power electronic devicesin a motor drive includes a base plate, a plurality of power electronicdevices, and a sensor. Each power electronic device is mounted to thebase plate and mounted proximate to each other within the integratedmotor drive, and the sensor generates a digital signal corresponding toa measured temperature within the integrated motor drive. Thetemperature detection system also includes a circuit board, having afront surface and a rear surface, where the rear surface is mounted tothe base plate, the front surface is configured to receive the sensor,and the sensor is located on the circuit board proximate to the powerelectronic devices. A copper pad is mounted on the front surface of thecircuit board defining a thermally conductive path between the circuitboard and the sensor.

According to another embodiment of the invention, a power converter forcontrolling operation of a motor and configured to be mounted to themotor includes a housing configured to be mounted to a surface of themotor. The power converter includes an input connection and at least oneoutput connection. The input connection is mounted in the housing andconfigured to receive a DC voltage greater than 50 volts, and at leastone output is configured to be electrically connected to the motor. Eachoutput extends between an opening in the housing and an opening in thesurface of the motor to which the housing is mounted. A DC bus iselectrically connected between the input connection and an invertersection. The inverter section includes at least one power switchingdevice, configured to selectively connect the DC bus to one of theoutputs. The power converter further includes a base plate at leastpartially enclosed within the housing and a circuit board mounted to thebase plate. Each of the power switching devices is mounted to the baseplate. A sensor generates a digital signal corresponding to a measuredtemperature, where the sensor is mounted to the circuit board proximateto one of the power switching devices, and a processor is mounted on thecircuit board and configured to receive the digital signal from thesensor.

According to yet another embodiment of the invention, a method ofdetermining a junction temperature of a power electronic device in anintegrated motor drive is disclosed. The power electronic device ismounted to a base plate within the integrated motor drive. The methodincludes the steps of mounting a circuit board on the base plate andmounting a sensor on the portion of the circuit board proximate to thepower electronic device. At least a portion of the circuit board isproximate to the power electronic device, and the circuit board includesa thermally conductive pad between the sensor and a top surface of afirst layer of the circuit board. A digital signal is generated from thesensor, corresponding to a temperature measured by the sensor. Thedigital signal is received by a processor, and the processor uses athermal model of heat transfer between the power electronic device andthe sensor to determine an estimate of the junction temperature of thepower electronic device as a function of the thermal model and of thedigital signal from the sensor.

These and other advantages and features of the invention will becomeapparent to those skilled in the art from the detailed description andthe accompanying drawings. It should be understood, however, that thedetailed description and accompanying drawings, while indicatingpreferred embodiments of the present invention, are given by way ofillustration and not of limitation. Many changes and modifications maybe made within the scope of the present invention without departing fromthe spirit thereof, and the invention includes all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary embodiments of the subject matter disclosed herein areillustrated in the accompanying drawings in which like referencenumerals represent like parts throughout, and in which:

FIG. 1 is an exemplary motor control system illustrating a pair ofintegrated motor drives incorporating the present invention;

FIG. 2 is a schematic representation of the motor control system of FIG.1;

FIG. 3 is a schematic representation of an inverter section of FIG. 2.

FIG. 4 is a block diagram representation of a portion of one of theintegrated motor drives of FIG. 1; and

FIG. 5 is a partial cross-sectional view of one of the integrated motordrives of FIG. 1.

In describing the various embodiments of the invention which areillustrated in the drawings, specific terminology will be resorted tofor the sake of clarity. However, it is not intended that the inventionbe limited to the specific terms so selected and it is understood thateach specific term includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose. For example, the word“connected,” “attached,” or terms similar thereto are often used. Theyare not limited to direct connection but include connection throughother elements where such connection is recognized as being equivalentby those skilled in the art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning initially to FIG. 1, an exemplary embodiment of a distributedmotor control system 10 includes a power interface module 12, a pair ofmotors 14, and a pair of integrated motor drives 30. Each integratedmotor drive 30 includes a housing 32 configured to mount the integratedmotor drive 30 to one of the motors 14. It is contemplated that thedistributed control system 10 may include various other numbers ofmotors 14 and integrated motor drives 30. A first communication cable 16is connected between the power interface module 12 and a firstcommunication connector 17 on the first integrated motor drive 30. Asecond communication cable 18 connects a second communication connector19 from the first integrated motor drive 30 to the first communicationconnector 17 on the second integrated motor drive 30. Similarly,additional second communication cables 18 may be provided to connectadditional integrated motor drives 30, if provided, in the distributedmotor control system 10. A communications terminating connector 20 isprovided on the second communication connector 19 of the finalintegrated motor drive 30 in the distributed motor control system 10. Afirst power cable 22 is connected between the power interface module 12and a first power connector 23 on the first integrated motor drive 30. Asecond power cable 24 connects a second power connector 25 from thefirst integrated motor drive 30 to the first power connector 23 on thesecond integrated motor drive 30. Similarly, additional second powercables 24 may be provided to connect additional integrated motor drives30, if provided, in the distributed motor control system 10. A powerterminating connector 26 is provided on the second power connector 25 ofthe final integrated motor drive 30 in the distributed motor controlsystem 10. According to various embodiments of the invention, it iscontemplated that the first and second communication connectors, 17 and19 respectively, may be identical connectors, the first and secondcommunications cables, 16 and 18 respectively, may be identical cablesof the same or of varying length, the first and second power connectors,23 and 25 respectively, may be identical connectors, and the first andsecond power cables, 22 and 24 respectively, may be identical cables ofthe same or of varying length.

Referring next to FIG. 2, the power interface module 12 includes arectifier section 40, connected in series between the input voltage 13and a DC bus 42, and a DC bus capacitor 48 connected across the DC bus42. It is understood that the DC bus capacitor 48 may be a singlecapacitor or multiple capacitors connected in parallel, in series, or acombination thereof. The rectifier section 40 may be either passive oractive, where a passive rectifier utilizes electronic devices such asdiodes, which require no control signals, and an active rectifierutilizes electronic devices, including but not limited to transistors,thyristors, and silicon controlled rectifiers, which receive switchingsignals to turn on and off. The power interface module 12 also includesa processor 50 and a memory device 52. It is contemplated that theprocessor 50 and memory device 52 may each be a single electronic deviceor formed from multiple devices. Optionally, the processor 50 and/or thememory device 52 may be integrated on a field programmable array (FPGA)or an application specific integrated circuit (ASIC). The processor 50may send and/or receive signals to the rectifier section 40 as requiredby the application requirements. The processor 50 is also configured tocommunicate with external devices via an industrial network 15,including but not limited to, DeviceNet, ControlNet, or Ethernet/IP andits respective protocol. The processor 50 further communicates withother devices within the motor control system 10 via any suitablecommunications medium, such as a backplane connection or an industrialnetwork, which may further include appropriate network cabling androuting devices.

The DC bus 42 includes a first voltage rail 44 and a second voltage rail46. Each of the voltage rails, 44 or 46, are configured to conduct a DCvoltage having a desired potential, according to applicationrequirements. According to one embodiment of the invention, the firstvoltage rail 44 may have a DC voltage at a positive potential and thesecond voltage rail 46 may have a DC voltage at ground potential.Optionally, the first voltage rail 44 may have a DC voltage at groundpotential and the second voltage rail 46 may have a DC voltage at anegative potential. According to still another embodiment of theinvention, the first voltage rail 44 may have a first DC voltage at apositive potential with respect to the ground potential and the secondvoltage rail 46 may have a second DC voltage at a negative potentialwith respect to the ground potential. The resulting DC voltage potentialbetween the two voltage rails, 44 and 46, is the difference between thepotential present on the first voltage rail 44 and the second voltagerail 46.

According to one embodiment of the invention, the DC bus 42 of the powerinterface module 12 is connected in series with the DC bus 42 of each ofintegrated motor drives 30. Electrical connections are establishedbetween the respective DC buses 42 via the power cable 22, 24 totransfer the DC bus voltage between devices. Each integrated motor drive30 further includes a processor 54 and a memory device 56. It iscontemplated that the processor 54 and memory device 56 may each be asingle electronic device or formed from multiple devices. Optionally,the processor 54 and/or the memory device 56 may be integrated on afield programmable array (FPGA) or an application specific integratedcircuit (ASIC).

The DC voltage on the DC bus 42 is converted to an AC voltage by aninverter section, 60. According to one embodiment of the invention, eachinverter section 60 converts the DC voltage to a three-phase outputvoltage available at an output 66 connected to the respective motor 14.The inverter section 60 includes multiple switches 61 which selectivelyconnect one of the output phases to either the first voltage rail 44 orthe second voltage rail 46. Referring also to FIG. 3, each switch 61 mayinclude a transistor 62 and a diode 64 connected in parallel to thetransistor 62. Each transistor 62 receives a switching signal 68 toenable or disable conduction through the transistor 62 to selectivelyconnect each phase of the output 66 to either the first voltage rail 44or the second voltage rail 46 of the DC bus 42.

Referring next to FIG. 4, each integrated motor drive 30 includes a baseplate 80 mounted within the housing 32. The base plate 80 is constructedof a thermally conductive material such as a metal. According to oneembodiment of the invention, the base plate 80 is made from copper. Asillustrated, a circuit board 70 is mounted over the base plate 80 andhas an outer periphery 73 that is equal to or greater than the outerperiphery of the base plate 80. Optionally, the outer periphery of thebase plate 80 may be greater than the outer periphery 73 of the circuitboard 70. It is contemplated that the circuit board 70 may be a singlecircuit board or multiple circuit boards mounted to and covering variousportions of the base plate 80. Optionally, the circuit board 70 mayfurther include multiple boards, mounted one over the other or invarious other configurations without deviating from the scope of theinvention. The base plate 80 is exposed through an opening 72 in thecircuit board 70. Each of the power electronic devices (e.g., the IGBT62 and the FWD 64) are mounted to the base plate 80, also referred to asdirect bonded copper (DBC) devices. A temperature sensor 58 is mountedto the circuit board 70 proximate to the opening 72 and, therefore,proximate to the power electronic devices 62, 64. According to oneembodiment of the invention, the temperature sensor 58 is located within5.0 cm, preferably within 1.5 cm, and more preferably about 0.6 cm fromthe power electronic devices. The temperature sensor 58 generates adigital signal 55 corresponding to the measured temperature which may beprovided to the processor 54. The processor 54, executing a programstored in the memory device 56, may be configured to monitor the digitalsignal 55 from the temperature sensor 58 and generate alerts and/or shutdown operation of the integrated motor drive 30 as a function of themeasured temperature.

Referring next to FIG. 5, each of the power electronic devices includesa bare die power electronic device 82, such as an IGBT or FWD, mountedto a first copper layer 86 via solder 84. A ceramic layer 90 separatesthe first copper layer 86 from a second copper layer 88, and the secondcopper layer 88 is, in turn, mounted to the base plate 80 via solder 92.The first copper layer 86 may be etched to form conductive paths, ortraces, between multiple power electronic devices 82 mounted to thefirst copper layer 86. The ceramic layer 90 provides an electricallyinsulating layer between the first and second copper layers, 86 and 88respectively. The second copper layer 88 may be, for example, a groundplane.

According to the illustrated embodiment, the circuit board 70 is amulti-layer board and, more specifically, includes four layers 74.Optionally, the circuit board 70 may include six, or any other suitablenumber of layers 74 according to the application requirements. Thecircuit board 70 is secured to the copper base plate by glue or by anyother suitable fastener, for example, via mounting screws. A layer ofglue and dielectric grease 71 may be included between the circuit board70 and the base plate 80 to secure the circuit board 70 and to provide athermally conductive layer between the circuit board 70 and the baseplate 80. The temperature sensor 58 includes a body 53 from which leads57 extend. The leads 57 are secured to the first layer 74 of the circuitboard 70 by solder joints 59 according to methods understood in the art.A first copper pad 78 is located on the first layer 74 of the circuitboard 70 between the front side of the first layer 74 and the rear sideof the temperature sensor 58. Additional copper pads 76 are locatedbetween each of the layers 74 of the circuit board 70 positioned betweenthe temperature sensor 58 and the base plate 80. Multiple vias 77 arealso located between the temperature sensor 58 and the base plate 80.The vias 77 extend through one or more layers 74 of the circuit board 70and, preferably, extend through each layer 74 of the circuit board 70except the layer 74 secured to the base plate 80. The first copper pad78, additional copper pads 76, and vias 77 are, preferably, electricallyisolated from circuit components mounted on the circuit board 70.

In operation, the power interface module 12 receives an AC input voltage13 and converts it to a DC voltage with the rectifier section 40. The ACinput voltage 13 may be either a three phase or a single phase ACvoltage. If the rectifier section 40 is an active rectifier, theprocessor 50 will receive signals from the active rectifiercorresponding to, for example, amplitudes of the voltage and current onthe AC input and/or the DC output. The processor 50 then executes aprogram stored in memory 52 to generate switching signals to activateand/or deactivate the switches in the active rectifier, where theprogram includes a series of instructions executable on the processor50. In addition, the switching signals may be generated such that powermay be transferred in either direction between the AC input and the DCoutput. Whether there is a passive rectifier or an active rectifier, theDC bus capacitor 48 connected across the DC bus 42 reduces the rippleresulting from the voltage conversion. The DC voltage is then providedvia the DC bus 42 between the power interface module 12 and subsequentintegrated motor drives 30. The level of DC voltage transferred via theDC bus 42 is typically greater than 50 volts and may be, for example, atleast 325 VDC if the AC input voltage 13 is 230 VAC or at least 650 VDCif the AC input voltage 13 is 460 VAC.

The processor 50 of the power interface module 12 may further beconfigured to communicate with other external devices via the industrialnetwork 15. The processor 50 may receive command signals from a userinterface or from a control program executing, for example, on anindustrial controller. The command signals may include, but are notlimited to, speed, torque, or position commands used to control therotation of each motor 14 in the distributed motor control system 10.The processor 50 may either pass the commands directly or execute astored program to interpret the commands and subsequently transmit thecommands to each integrated motor drives 30. The processor 50communicates with the processors 54 of the integrated motor drives 30either directly or via a daisy chain topology and suitable networkcables 16, 18. Further, the processor 50 may either communicate usingthe same network protocol with which it received the commands via theindustrial network 15 or convert the commands to a second protocol fortransmission to the integrated motor drives 30.

Each integrated motor drive 30 converts the DC voltage from the DC bus42 to an AC voltage suitable to control operation of the motor 14 onwhich it is mounted. The processor 54 executes a program stored on amemory device 56. The processor 54 receives a reference signal via thecommunications medium 16 or 18 identifying the desired operation of themotor 14. The program includes a control module configured to controlthe motor 14 responsive to the reference signal and responsive tofeedback signals such as voltage sensors, current sensors, and/or theangular position sensors mounted to the motor 14. The control modulegenerates a desired voltage reference signal and provides the desiredvoltage reference signal to a switching module. The switching moduleuses, for example, pulse width modulation (PWM) to generate theswitching signals 68 to control the switches 61 responsive to thedesired voltage reference signal.

In order to protect the switches 61 in the inverter section 60, theprocessor 54 monitors the temperature signal 55 generated by thetemperature sensor 58. The processor 54 then determines an estimate ofthe temperature of the switches as a function of the temperature signal55 and of a thermal model of the heat transfer path between thetemperature sensor 58 and the switches 61. It is contemplated that asingle thermal model may be determined to generate a single temperatureestimate. Optionally, separate thermal models may be determined togenerate temperature estimates for each of the power electronic devices.According to still another embodiment of the invention, a first thermalmodel may be determined to generate an estimated junction temperature ofthe IGBTs 62 and a second thermal model may be determined to generate anestimated junction temperature of the FWDs 64.

Each thermal model includes three primary thermal impedances. A firstthermal impedance is determined for the transfer of heat between thebare die power electronic device 82 and the base plate 80. A secondthermal impedance is determined for the transfer of heat between thebase plate 80 and the temperature sensor 58. Inclusion of the firstcopper pad 78, additional copper pads 76, and vias 77 improves thethermal conductance between the base plate 80 and the temperature sensor58 or, conversely, reduces the thermal impedance between the base plate80 and the temperature sensor 58. The third thermal impedance existsinside the base plate 80 from the location below the IGBTs 62 or theFWDs 64 and the location below the temperature sensor 58. Because thetemperature sensor 58 is placed proximate to the IGBTs 62 and the FWDs64 and because the base plate 80 has a high thermal conductance, thethird thermal impedance is much less than first and the second thermalimpedance.

Each thermal model is also a function of the power dissipated in thecorresponding power electronic device. The power electronic devicesincur both switching losses and conduction losses which are primarilydissipated within the device as heat. The magnitude of the switchingloss and conduction loss are additionally a function of the currentconducted through the device. The processor 54 monitors at least onefeedback signal corresponding to the current output to the motor 14 andmay determine an average power loss in each of the IGBTs 62 and/or theFWDs 64. In addition, distribution of power losses among the powerelectronic devices may vary at varying frequency of output voltage tothe motor 14. According to one embodiment of the invention, theprocessor 54 monitors at least one of a speed command or a speedfeedback signal to determine the speed of the motor 14 and may furtherutilize the speed information in each of the first and second thermalmodels. According to another embodiment of the invention, the processor54 may monitor a commanded frequency of the output voltage to the motor14 and determine the speed of the motor. According to still anotherembodiment of the invention, BF_(—I)(f) and BF_(—D)(f) may be determinedas frequency dependent compensation factors and the commanded outputfrequency may be utilized directly by each thermal model. The processor54 then determines the temperature of the IGBTs 62 as a function of thefirst thermal model and determines the temperature of the FWDs 64 as afunction of the second thermal model.

It should be understood that the invention is not limited in itsapplication to the details of construction and arrangements of thecomponents set forth herein. The invention is capable of otherembodiments and of being practiced or carried out in various ways.Variations and modifications of the foregoing are within the scope ofthe present invention. It also being understood that the inventiondisclosed and defined herein extends to all alternative combinations oftwo or more of the individual features mentioned or evident from thetext and/or drawings. All of these different combinations constitutevarious alternative aspects of the present invention. The embodimentsdescribed herein explain the best modes known for practicing theinvention and will enable others skilled in the art to utilize theinvention

We claim:
 1. A temperature detection system for estimating a junctiontemperature of power electronic devices in a motor drive, the systemcomprising: a base plate; a plurality of power electronic devices, eachpower electronic device mounted to the base plate and mounted proximateto each other within the integrated motor drive; a sensor generating adigital signal corresponding to a measured temperature within theintegrated motor drive; a circuit board having a front surface and arear surface, wherein the rear surface is mounted to the base plate andthe front surface is configured to receive the sensor and wherein thesensor is located on the circuit board proximate to the power electronicdevices; and a copper pad on the front surface of the circuit boarddefining a thermally conductive path between the circuit board and thesensor.
 2. The temperature detection system of claim 1 wherein thecircuit board includes a plurality of layers and a plurality of copperpads between each of the layers and aligned with the copper pad on thefront surface.
 3. The temperature detection system of claim 1 whereinthe circuit board includes a plurality of layers and a plurality of viasextending through at least a portion of the layers between the baseplate and the sensor.
 4. The temperature detection system of claim 3wherein the circuit board further includes a plurality of additionalcopper pads between each of the layers and aligned with the copper padon the front surface.
 5. The temperature detection system of claim 4wherein, the copper pad, each of the additional copper pads, and each ofthe vias between the sensor and the base plate are isolated fromelectrically conductive traces on the circuit board.
 6. The temperaturedetection system of claim 1 further comprising: a memory deviceconfigured to store a series of instructions and at least one thermalmodel; and a processor configured to receive the digital signal from thesensor and configured to execute the series of instructions to determinea temperature as a function of the thermal model and of the digitalsignal.
 7. The temperature detection system of claim 6 wherein thethermal model is a function of at least one of an average power loss inthe power electronic devices during operation and a frequency of avoltage output to a motor connected to the integrated motor drive. 8.The temperature detection system of claim 1 wherein the sensor islocated less than 1.5 cm from the power electronic devices.
 9. A powerconverter for controlling operation of a motor, the power converterconfigured to be mounted to the motor, the power converter comprising: ahousing configured to be mounted to a surface of the motor; an inputconnection mounted in the housing and configured to receive an inputvoltage; at least one output configured to be electrically connected tothe motor, each output extending between an opening in the housing andan opening in the surface of the motor to which the housing is mounted;a DC bus electrically connected between the input connection and aninverter section, wherein the inverter section includes at least onepower switching device, each power switching device configured toselectively connect the DC bus to one of the outputs; a base plate atleast partially enclosed within the housing, wherein each of the powerswitching devices is mounted to the base plate; a circuit board mountedto the base plate; a sensor generating a digital signal corresponding toa measured temperature, wherein the sensor is mounted to the circuitboard proximate to one of the power switching devices; and a processorconfigured to receive the digital signal from the sensor.
 10. The powerconverter of claim 9 further comprising a first copper pad on thecircuit board defining a thermally conductive path between the circuitboard and the sensor.
 11. The power converter of claim 10 wherein thecircuit board includes a plurality of layers and a plurality ofadditional copper pads, each additional copper pad mounted on one of thelayers and aligned with the first copper pad.
 12. The power converter ofclaim 9 wherein the circuit board includes a plurality of layers and aplurality of vias extending through at least a portion of the layersbetween the base plate and the sensor.
 13. The power converter of claim12 wherein the circuit board further includes a plurality of additionalcopper pads, each additional copper pad mounted on one of the layers andaligned with each of the other additional copper pads between the sensorand the base plate.
 14. The power converter of claim 9 furthercomprising a memory device configured to store a series of instructionsand at least one thermal model and wherein the processor is furtherconfigured to execute the series of instructions to determine atemperature as a function of the thermal model and of the digitalsignal.
 15. The power converter of claim 14 wherein the thermal model isa function of at least one of an average power loss in the powerswitching devices during operation and a speed of rotation of the motorconnected to the integrated motor drive.
 16. The power converter ofclaim 9 wherein the sensor is located less than 1.5 cm from the powerswitching devices.
 17. A method of determining a junction temperature ofa power electronic device in an integrated motor drive, wherein thepower electronic device is mounted to a base plate within the integratedmotor drive, the method comprising the steps of: mounting a circuitboard on the base plate, wherein at least a portion of the circuit boardis proximate to the power electronic device; mounting a sensor on theportion of the circuit board proximate to the power electronic device,wherein the circuit board includes a thermally conductive pad betweenthe sensor and a front surface of a first layer of the circuit board;generating a digital signal from the sensor corresponding to atemperature measured by the sensor; receiving the digital signal with aprocessor; obtaining a thermal model of heat transfer between the powerelectronic device and the sensor from a memory device in communicationwith the processor; and determining the junction temperature of thepower electronic device by the processor as a function of the thermalmodel and of the digital signal from the sensor.
 18. The method of claim17 further comprising the step of determining an average power loss ofthe power electronic device during operation of the integrated motordrive, wherein the junction temperature is determined as a function ofthe thermal model, the digital signal, and the average power loss. 19.The method of claim 17 further comprising the step of determining afrequency of a voltage output to a motor connected to the integratedmotor drive, wherein the junction temperature is determined as afunction of the thermal model, the digital signal, and the frequency ofthe voltage output to the motor.
 20. The method of claim 17 furthercomprising the steps of: determining an average power loss of the powerelectronic device during operation of the integrated motor drive; anddetermining a frequency of a voltage output to a motor connected to theintegrated motor drive, wherein the junction temperature is determinedas a function of the thermal model, the digital signal, the averagepower loss, and the frequency of the voltage output to the motor.